At present, among various batteries, a lithium ion battery is attracting attention from the standpoint that the energy density is high. Above all, the attention is focused on an all-solid secondary battery in which an electrolytic solution is replaced by a solid electrolyte. The reason therefor is that unlike a secondary battery using an electrolytic solution, the all-solid secondary battery using no electrolytic solution does not cause decomposition, etc. of an electrolytic solution attributable to overcharge and has high cycle durability and high energy density.
Meanwhile, it is known that when a secondary battery is charged and left standing, the electromotive force decreases. One of causes thereof is a self-discharge due to a minor short circuit, etc. formed inside the battery. In view of battery efficiency, the self-discharge amount is preferably small. To cope with this, there is known a manufacturing method where a battery manufactured is measured for the self-discharge amount and a battery unsuitable for a product is eliminated to maintain the quality of the whole product.
Specific examples of the method for inspecting the self-discharge amount of a battery include the method of Patent Document 1. In addition, specific examples of the method for manufacturing a battery including a method for inspecting the self-discharge amount of a battery include the method of Patent Document 2. Both methods of Patent Documents 1 and 2 relate to a battery using an electrolytic solution.
Specifically, in Patent Document 1, with respect to a solid secondary battery using an electrolytic solution, the open-circuit voltage of a battery after charging the battery is measured, the battery is constant-voltage charged such that the measured open-circuit voltage is maintained, and the self-discharge amount is calculated from the amount of current necessary for maintaining the open-circuit voltage at the time of constant voltage charge.
In Patent Document 2, with respect to a solid secondary battery using an electrolytic solution, initial charge is performed after the completion of assembly but before shipping the product, and then self-discharge inspection is performed. In the case where a minor short circuit is detected in the battery inspected, recharge/discharge is performed so as to remove the minor short circuit.